1. Field of the Invention
The present invention relates to a method and an apparatus for determining the conformity of an attached telecommunication device to test procedures and, more particularly, to a method and apparatus for aligning G.706 frames and multiframe and handling a Cyclic Redundancy Check (CRC) procedure test.
2. Background Art
Any G.706 telecommunication adapter or device designed for the European market needs to comply with the CCITT G.706 recommendation to be homologated. The CCITT G.706 defines for the E1 speed a number of specifications dedicated to the Cyclic Redundancy Check (CRC) handling and the frame synchronization.
FIG. 1 shows the format of E1 frames. An E1 multiframe is made of 16 consecutive E1 frames and lasts 2 ms. An E1 frame is made of 32 timeslots and lasts 125 us. Each timeslot or slot is 8-bits long. Timeslot 0 is dedicated to the frame and multiframe alignments and the CRC test, whereas the other timeslots 1-31 are dedicated to the users. A timeslot corresponds to each user.
FIG. 2 gives the E1 multiframe structure. Slot 0 of each frame carries a pattern. The even frames carry the Frame Alignment Signal (FAS) on bits 2-8 having a pattern `0011011` and are used for the frame alignment. The odd frames carry bit 2=1 and are used for the multiframe alignment checking. Bit A, which corresponds to a remote alarm indication, is carried on bit 3 of odd frames. Each sub-multiframe has a 4-bit (C1-C4) CRC of the E1 multiframe and are carried on even frames. The other bits, such as Bits Si, are spare bits for international usage (also called E-bits) and Bits Sn are spare bits for national usage are of less importance.